246 O. C. GLASER. 



2. The first change can be accounted for by the stretching 

 which the larvae undergo ; the second change is explained by a 

 fourfold increase in the number of cells found in transverse sec- 

 tions through the middle of the digestive tract. 



3. During this period of cell increase there was found a maxi- 

 mum of one mitotic division in 1,751 nuclei. 



4. During the same period of development, there was found a 

 minimum of 69 amitotic divisions. 



5. From this it follows that during the period of most active 

 cell multiplication more than 1 per cent, of all divisions is mitotic 

 and more than 98 per cent, are amitotic. 



6. Since there were found during the pre-cannibal, the cannibal, 

 and the post-cannibal periods, 152 cases of what is interpreted as 

 nuclear division, and since of these 20 were mitotic, it follows 

 that during the entire developmental period considered a little 

 over 1 3 per cent, of all the divisions were mitotic and a little less 

 than 87 per cent, amitotic. 



7. Therefore the conclusion is reached that amitosis plays in 

 this instance an important, if not the chief part in the differenti- 

 ation of a definitive tissue. 



8. Of the two alternatives which might be suggested, one, that 

 unobserved epidemics of mitosis account for the facts, is not only 

 without foundation, but is improbable ; the other, that a fourfold 

 increase in cells can be accounted for on the basis of 1 mitotic 

 division per 1,751 nuclei involves an absurdity. 



Postscript. 



By an oversight I have omitted a reference to Professor Har- 

 gitt's observations on the occurrence of amitotic divisions in the 

 development of certain ccelenterates. In his paper entitled 

 " The Organization and Early Development of the Egg of Clava 

 leptostyla Ag.," Biol. Bull., Vol. X., Hargitt says : " During the 

 early cleavage, even up to the sixteen-cell stage, no evidence of 

 mitosis has been found." Similar experiences were met with in 

 studying the development of Eudendriiun and Pennaria, and Pro- 

 fessor Hargitt adds : " as facts multiply . . . cytologists will be 

 forced to take cognizance of this form of cytogeny and give it 

 something more than a merely incidental place in cellular 

 activities." 



